As previously mentioned, you can edit Google's URL to customize how fresh the search results should be. For example, if you append &as_qdr=y9 to Google's search URL, you'll restrict the results to web pages first indexed by Google in the last 9 years. Since this restriction should include all web pages from Google's index, you can use it to display the timestamp next to each search result (e.g.: a search for iPod).

Maybe in the future Google will display the date next to each search result, it will try to approximate the date when a page has been created, allow users to filter results from certain periods and sort the results by date.